I picked up GW when it came out, convinced a significant portion of my FPS clan to pick it up as well. I played it pretty religiously for 3 months or so and then went back to WoW. Here are some pro/con thoughts for you.
GW-PvE:
Linear PvE, you don't get a whole lot of options
Instanced Everything, which is nice because there aren't any smacktards griefing you, but it isolates you as well.
Minimal Weapon/Gear itemization. For most people it's either max or it's worthless, no inbetween.
Once you visit a town once you can map back to it at the touch of a button, eliminating travel time completely.
GW-PvP:
Low level PvP is a joke, don't even bother. There aren't any limits set on weapons/armor/skills, so it's fully possible for a level 7 character to be strutting around the first tier PvP arena with end-game everything.
End-game PvP is fast, like really fast. You get your group together, click join and 3-5 minutes later you have either won or lost, ready for the next rung up on the ladder. Once you get to the top-tier the competition is fierce and intense. PvP is the true reason for buying this game. If Random Arenas aren't your thing Guild vs Guild battles are pretty intense as well, fighting in your own guildhall and whatnot.
GW vs. WoW
WoW is structured to keep you coming back every month for more. They have detailed and complex story lines, they have thousands of hours of content, they have 60 levels of chewy RPG goodness. With the right group you can finish the PvE portion of GW in a weekend, for serious. As much more MMO as WoW has over GW, GW is a much more social game. It is absolutely imperative that you get together with a good group of people or your interest in this game wanes after you have finished the PvE content on your second (or third) character. The benefit of no monthly fees is a huge win for GW, meaning that even if you don't want to keep going with it, you don't have to. Just put all of your stuff into storage and log off... It'll be there when you come back.
If you guys do pick this up (or already have it) you can find me in game on:
Reverend Jekyll
Reverend Burninate
or
Reverend Smashalot